Most of the motors with speed reducers of this kind are combinations of motors for generating rotational power and gear type speed reducers for reducing this rotational power in speed. The motors with speed reducers of this kind have the structure of reducing speed mechanically. The motors can thus be operated in most efficient conditions (range of the numbers of rotations), finding wide use in every industrial field.
In this case, most of (eight or more out of ten) prevailing gear type speed reducers are used within the range of {fraction (1/10)} to {fraction (1/60)} or so in total reduction ratio. As for the varieties of speed reducers, different types such as simple planetary gear speed reducers, oscillating internal meshing planetary gear speed reducers, bevel type speed reducers, hypoid speed reducers, and worm speed reducers are available in series so as to allow selection according to applications.
By the way, because of using gear type speed reducers, the series of motors with speed reducers of this kind has reduction ratios set at predetermined intervals (common ratios). Consequently, abundant variations of reduction ratios were not always available, and it was sometimes impossible to meet user needs finely.
In addition, each type of speed reducer was specialized in certain ranges of reduction ratios, and there was a limit to extending the range of reduction ratios of each type while suppressing the fabrication costs. Moreover, speed reducers covering higher reduction ratios were generally high in fabrication costs. If driving apparatuses of higher reduction ratios were required, then speed reducers of high-cost types were inevitably selected and combined with motors, which resulted in a problem of limited flexibility in selecting the types of speed reducers.
Aside from these problems, there were other problems that when gear type speed reducers were used, the meshing portions of the gears (in particular, the meshing portions between the input shafts rotating at high speed and the first-stage gears) produced high noise and vibration, and that the resonance between the speed-reducer side and the motor side might often make the overall noise level and vibration level of the motors with speed reducers higher than the noise from the units themselves.
In this regard, detailed description will be given in conjunction with an example of a geared motor that uses a conventionally-known oscillating internal meshing planetary gear structure (gearing corresponding to International Patent Classification F16H 1/32), which tends to cause particularly high noise/vibration levels, as the speed reducer.
FIG. 16 shows the example of the geared motor (a motor with a speed reducer) which includes an oscillating internal meshing planetary gear speed reducer described in Japanese Patent Laid-Open Publication No. Hei 5-231482. This geared motor 1 is an integrated combination of a speed reducer 2 and a motor 3.
The casing 51 of the speed reducer 2 consists of a center casing 52, a joint casing 53 closer to the motor 3, and a front casing 54 opposite from the motor 3. The casing 55 of the motor 3 consists of a cylindrical casing 56, the joint casing 53 closer to the speed reducer 2, and a rear cover 57 opposite from the speed reducer 2. In this case, the above-mentioned joint casing 53 doubles as parts of the casings 51, 55 of the speed reducer 2 and the motor 3. Through the medium of this joint casing 53, the speed reducer 2 and the motor 3 are connected in one.
The speed reducer 2 has a first shaft 11 to be an input shaft and a second shaft 12 to be an output shaft.
Two eccentric bodies 13a and 13b are fitted to the outer periphery of the first shaft 11 with a predetermined phase difference therebetween (180°, in this example). These eccentric bodies 13a and 13b make integral rotation with the first shaft 11. The centers of the eccentric bodies 13a and 13b are off the shaft axis of the first shaft 11 by predetermined eccentricities, respectively. External gears 15a and 15b are fitted to the outer peripheries of the eccentric bodies 13a and 13b, respectively. The external gears 15a and 15b have a plurality of inner pin holes 16a and 16b, respectively. Inner pins 17 are fitted into these inner pin holes 16a and 16b with play.
On the outer peripheries of the external gears 15a and 15b are formed external teeth of trochoidal tooth profile or arc tooth profile, which are in internal mesh with an internal gear 20. The internal gear 20 is integrally formed on the inner periphery of the center casing 52. The individual internal teeth thereof are made of outer pins 21 which are retained on the inner periphery of the center casing 52.
A pair of carriers 23 and 24 is arranged astride the external gears 15a and 15b. Both the carriers 23 and 24 are rotatably supported by bearings 31 and 32, and connected in one by a plurality of carrier pins (coupling pins) 25 and spacers 26.
The inner pins 17 are connected at both ends to the carriers 23 and 24 on both sides so as to be capable of sliding rotation. The rotation components of the external gears 15a and 15b are exclusively transmitted to the carriers 23 and 24 on both sides through the inner pins 17.
One end of the first shaft 11 lies in a center hole 23a in carrier 23 on the motor-3 side, and is connected to a motor shaft 61 through a coupling 70.
Having this configuration, this speed reducer can achieve a speed reduction of from the number of teeth of the external gears 15a, 15b to one by publicly-known actions.
Now, description will be given of another conventional example.
FIGS. 17 and 18 show a conventional geared motor described in Japanese Patent Laid-Open Publication No. Hei 10-299841. This geared motor 500 uses an oscillating internal meshing planetary gear speed reducer of so-called power-distributed shaft type.
This internal meshing planetary gear speed reducer comprises: a first shaft 502 to be connected to an external motor shaft 501; a plurality of power-distributed shafts 503 which are arranged on a circumference concentric with the first shaft 502 and rotate in conjunction with the first shaft 502; eccentric bodies 504 which are arranged on the plurality of power-distributed shafts 503, respectively; an external gear 505 which is arranged so as to be capable of eccentric rotation with respect to the first shaft 502; an internal gear 506 which is installed concentrically with the first shaft 502 and with which the external gear 505 meshes internally while making eccentric rotation about the first shaft 502; and a second shaft 507 coupled to the plurality of power-distributed shafts 503.
In this internal meshing planetary gear structure, the eccentric bodies 504 are arranged so as to lie between a pair of carriers 523 and 524. The power-distributed shafts 503 are rotatably supported by the carriers 523 and 524. Then, a sun roller 511 is arranged on the first shaft 502. A plurality of power-distributed rollers 512, each making external contact with the sun roller 511, are arranged on the plurality of power-distributed shafts 503 through spline connections, respectively. A press-contact ring 513 for the plurality of power-distributed rollers 512 to make internal contact with is arranged outside the power-distributed rollers 512. The press-contact ring 513 in this case is intended merely to produce a press-contacting force between the sun roller 511 and the power-distributed rollers 512, and thus differs from simple planetary rings in function.
Geared motors adopting such internal meshing planetary gear speed reducers as illustrated in the foregoing examples have the advantages of having a simple, compact structure with high rigidity and offering high reduction ratios. Nevertheless, the structure that the external gear(s) oscillates/oscillate while meshing with the mating gear has the problem that the vibration on the speed-reducer side and the vibration on the motor side combine to produce resonance, yielding an inevitable tendency toward higher noise.
More specifically, in the foregoing geared motors, the vibration occurring on the speed-reducer side vibrates the connected motors, and mixes with the vibration generated by the motors themselves to produce complex resonance. Moreover, the vibration sometimes returns to the originating speed reducers for more complex resonance, which might result in the production of higher noise from the entire geared motors on rare occasions.
In this regard, for the case of the geared motor 1 of FIG. 16, the motor shaft 61 and the first shaft 11 are in floating connection through the coupling 70 of spline type. Thereby, the vibration of the motor unit 3 itself and the vibration of the speed reducer 2 itself are blocked from mutual transmission, thereby preventing the two sides from producing resonance.
Merely establishing the floating connection through the coupling 70, however, could not suppress the mutual transmission of the vibrations significantly, and hence a sufficient noise reduction effect was not obtained.
Moreover, even in the geared motor adopting the internal meshing planetary gear structure of power-distributed shaft type of FIG. 17, the noise reduction effect as much as has been expected was not obtained in actual operation. The possible reason is as follows:
That is, in the structure of this power-distributed shaft type, the individual power-supply shafts 503 undergo vibration and deflection due to the oscillating movement of the external gear 505. The power-distributed shafts 503 are therefore quite likely to vibrate and deform (deflect) under the loads from this external gear 505. Meanwhile, in this geared motor, the power-distributed rollers 512 which make press-contact with the sun roller 511 exist on those power-distributed shafts 503. Consequently, the vibration and deformation of the power-distributed shafts 503 can be transmitted to the power-distributed rollers 512→ the sun roller 511 directly, thereby hindering the effect of blocking vibration transmission which originates from the use of the friction rollers. In other words, the cause seems to consist in that the rollers 512 suited to high-speed low-torque power transmission are arranged directly on the power-distributed shafts 503 which undergo the direct effect of deformation due to the load transmission in the internal meshing planetary gear structure.
In any case (leaving the cause aside), the foregoing two examples, despite the adoption of the floating connection and the incorporation of the friction rollers, have not gone far enough to achieve such a noise improving effect as renews the established ideas of geared motors.
In regard to such increases in noise and vibration level, the use of the other types of speed reducers also ended up with similar results.